Reusable thermal protection is a technology used to enable long duration hypersonic flights. Transpiration cooling has been demonstrated to be a promising active cooling technique in terms of coolant mass requirements and disturbance of the external flow. A methodology for the non-intrusive characterization of the local effective permeability of a complex carbon-carbon porous structure is described herein. The concept of effective permeability, which can be considered as the local blowing capability of a porous structure with respect to a selected coolant fluid, is also discussed. Specifically, the coolant (air) mass flux blown from a conical porous surface can be measured by a hot-film probe at a distance specified by an appropriate reference elementary area and the Reynolds number based on the diameter of the channels.
These measurements can be related to the pressure gradient across the local thickness of the material by using Darcy's law. Measurements can reveal a higher effective permeability near the nose of the cone where two longitudinal delaminations are identified. In one embodiment, the asymmetric blowing capability of the cone highlights an importance of characterizing the entire thermal protection system when contrasted with defining the overall properties of the material, which can be different at the full-scale level due to the geometry, the system integration (i.e. structural constraints), and the intrinsic defectology coming from the manufacturing process. In one example, the mass fluxes measured on the external porous surface supported the numerical aerothermal rebuilding of a wind-tunnel experiment on a transpiration cooling.